Supplementing low-protein beverages with leucine can produce the same level of muscle synthesis in young men as a beverage with five times the protein levels, says a new study.

Adding five grams of leucine to a beverage containing 6.25 grams of protein resulted in the same myofibrillar protein synthesis as a 25 gram dose of protein, report researchers from McMaster University in Canada and the Nestlé Research Centre, Nestec Ltd in Switzerland.

“These findings show that, within the context of mixed macronutrient intake, suboptimal protein doses can be made more effective in stimulating [myofibrillar protein synthesis] through the addition of a high proportion of free leucine,” wrote the researchers, led by Tyler Churchward-Venne from McMaster.

The result, which would allow formulators to achieve significant muscle dose with significantly lower levels of protein, have “important implications for formulations of protein beverages designed to enhance muscle anabolism”, they added.

‘Leucine is the trigger’

Leucine is described as the trigger for muscle protein synthesis by Ralf Jaeger, PhD, FISSN, President of Milwaukee-based consultancy Increnovo LLC.

“Protein supplementation has been shown to increase muscle protein synthesis in response to exercise in a dose-dependent manner,” Dr Jaeger told us, “and approximately 20g of protein are needed to robustly build more muscle than the gains we see from resistance training alone.

“Churchward-Venne et al. showed that suboptimal protein intake can be compensated by supplemental leucine. The results of this study add to the existing scientific body of evidence on leucine, a powerful nutritional activator of muscle protein synthesis and will aid food, beverage and supplement formulators to create products for optimal muscle protein synthesis with low-dose amounts of protein, or protein sources with naturally lower leucine content and/or reduced absorption.

“If the results seen in young healthy individuals can be translated to sarcopenia, the degenerative loss of skeletal muscle mass, remains to be seen, as the efficacy of leucine is reduced with age.”

Is more better?

Jose Antonio, PhD, CEO of the International Society of Sports Nutrition, told NutraIngredients-USA that the study partly answers the question of whether ‘more is better’. That is, 6.25 grams of whey protein plus a high dosage of leucine (5 grams) was more anabolic that the same dose of whey but with less leucine (3 grams).

“Interestingly, consuming 6.25 grams of whey plus 5 grams of leucine produced muscle protein synthesis rates similar to consuming 25 grams of whey protein (which naturally contains 3 g of leucine). So a suboptimal dose of whey protein can be compensated for by increasing leucine levels,” said Dr Antonio.

“From a product standpoint, it makes perfect sense to boost the amount of leucine added to protein powders. I imagine this would particularly help vegan protein sources such as rice, pea, hemp and others.”

Study details

Writing in the American Journal of Clinical Nutrition, Churchward-Venne and his co-workers assessed the effect of supplementing a lower-protein beverage (6.25 grams of whey protein and containing 0.75 grams of leucine) with 3 or 6 grams of leucine or a mixture of branched chain amino acids (BCAAs) – leucine, iso-leucine, valine – to 5.0 g total leucine, on muscle protein synthesis, and compared this with a high protein beverage (25 grams of whey protein providing 3 grams of leucine).

Forty men with an average age of 21 were recruited to participate in the study, and muscle synthesis was measured both under resting conditions and exercising conditions.

Results showed that the rates of muscle synthesis were increased by the greatest amount after the high protein beverage (about 267%) and the low protein plus 5 grams of leucine beverage (about 220%).

“Our current results extend those of our previous work [J Physiol. 2012, Vol. 590, pp. 2751–65) by showing that, within the context of a mixed macronutrient beverage, a suboptimal protein dose (6.25 g) supplemented with a higher proportion of leucine (5.0 g total) was as effective at stimulating increased [myofibrillar protein synthesis] rates as a dose of protein (25 g) able to induce a maximal stimulation of [myofibrillar protein synthesis] rates after resistance exercise and a dose of [essential amino acids] that maximally stimulates [myofibrillar protein synthesis] at rest,” wrote Churchward-Venne and his co-authors.